# Giant Direct and Inverse Electrocaloric Effects in Multiferroic Thin Films

## TL;DR

This study predicts giant room-temperature electrocaloric effects in multiferroic BiCoO₃ thin films, with tunable direct and inverse responses driven by electric field orientation, promising for environmentally friendly on-chip cooling technologies.

## Contribution

It introduces the prediction of large electrocaloric effects in BiCoO₃ thin films at room temperature, highlighting the role of spin-phonon coupling and phase competition, and demonstrates tunability via epitaxial strain.

## Key findings

- Giant electrocaloric effects predicted at room temperature in BiCoO₃ thin films.
- Electrocaloric response can be tuned by electric field orientation and epitaxial strain.
- Dual (direct and inverse) electrocaloric effects enable advanced cooling cycle designs.

## Abstract

Refrigeration systems based on compression of greenhouse gases are environmentally threatening and cannot be scaled down to on-chip dimensions. In the vicinity of a phase transition caloric materials present large thermal responses to external fields, which makes them promising for developing alternative solid-state cooling devices. Electrocaloric effects are particularly well-suited for portable refrigeration applications; however, most electrocaloric materials operate best at non-ambient temperatures or require the application of large electric fields. Here, we predict that modest electric fields can yield giant room-temperature electrocaloric effects in multiferroic BiCoO$_{3}$ (BCO) thin films. Depending on the orientation of the applied field the resulting electrocaloric effect is either direct (heating) or inverse (cooling), which may enable the design of enhanced refrigeration cycles. We show that spin-phonon couplings and phase competition are the underlying causes of the disclosed caloric phenomena. The dual electrocaloric response of BCO thin films can be effectively tuned by means of epitaxial strain and we anticipate that other control strategies like chemical substitution are also possible.